With reference to FIG. 1, scaffolds of steel usually comprise two frames 1 formed from vertical poles 11 and horizontal rods 12, and connecting members 13 arranged crosswise between the frames 1 and detachably held thereto. The vertical poles 11 are provided with retaining devices 2 for retaining the ends of the connecting members 13 thereon.
The retaining device 2 must be so adapted that the connecting member 13, once mounted thereon, can be held in place during usual use but is still easily detachable therefrom when disassembling the scaffold. FIGS. 7 and 8 show conventional retaining devices which fulfil the above requirement.
The retaining device 2a shown in FIG. 7 comprises a rod portion 41 having a base end to be secured to the main frame 1 and a forward end formed with a groove 3. A pivotable plate 31 fitted in the groove 3 is supported by a pin 32 at a position slightly away from its center of gravity toward the base end of the plate 31. The rod portion 41 is welded at its base end to the main frame 1 with the groove 3 positioned in parallel to a vertical plane.
Accordingly the pivotable plate 31 is at right angles with the rod portion 41 with its forward end always facing down under gravity. When holding the connecting member 13, the forward end of the pivotable plate 31 is raised to align the plate 31 with the rod portion 41, and the connecting member 13 is placed onto the rod portion 41 through an end hole 14. When the connecting member 13 has fitted to the rod portion 41 over the groove 3, the pivotable plate 31 returns to its original position under gravity, preventing the member 13 from slipping off the rod portion.
The retaining device 2b shown in FIG. 8 comprises a hollow rod portion 41 to be secured to the frame 1 and formed with an axial slit 33. A pawl plate 34 fitted in the slit 33 is projectable from and retractable into the rod portion. On one side of the rod portion opposite to the slit 33, the rod portion is indented from outside to provide a stopper 35 for the pawl plate 34 for preventing the plate from slipping off. A leaf spring 5 housed in the rod portion 41 biases the pawl plate 34 outward. The rod portion 41 is welded at its base end to the frame 1.
To mount the connecting member 13 on the device 2b, the member 13 is passed over the forward end of the rod portion 41 through a hole 14 of the member 13 and forced toward the base end of the rod portion 41. The pawl plate 34 therefore retracts into the portion 41 against the spring 5 and thereafter returns upon the member 13 passing over the pawl plate 34, preventing the connecting member 13 from slipping off.
Although the two retaining devices 2a and 2b have the advantage that the connecting member 13 is easily mountable on and detachable from the rod portion, they are difficult and expensive to make since the groove 3 and slit 33 must be formed by machining as by milling. The former device, in which the pivotable plate 31 is adapted to be raised to an upright position by the force of gravity, involves the necessity of welding the rod portion to the frame 1 with the groove 3 in parallel to a vertical plane. This procedure requires care and is cumbersome.
With the latter device, the rod portion having the pawl plate 34 fitted in the slit 33 must be indented from outside with a chisel to form the stopper 35 on one side thereof opposed to the slit 33. This procedure is difficult to follow.
Further when the frame 1 provided with retaining devices 2a or 2b is subjected to hot dipping or coating operation for the inhibition of corrosion, the operation entails the problem that the molten metal or coating composition ingressing into a clearance between the plate 31 or 34 and the cutout portion 3 or 33 solidifies, restraining the plate 31 or 34 against pivotal movement.